The present invention relates to a phase inverter circuit, and more specifically, to a phase inverter circuit having an input balun circuit and having a replica switched amplification stage to load the input balun circuit in parallel with the actual switched amplification stage of the phase inverter.
A phase inverter is a circuit that includes an input terminal, an output terminal and one bit control terminal. Typically, the input and output signals are single ended signals. A phase inverter creates a 180 degrees phase difference of the output signals when the control bit is being toggled between the “ON” and “OFF” states.
A “balun” or “balanced to unbalanced” circuit is a common electrical or electronic circuit that comes in many different types or forms. A balun may be used as part of a phase inverter circuit that converts a single ended input signal into a differential output signal (i.e., phase inverted or 180 degrees out of phase).
The phase inverter may include a switched amplification stage or circuit at the output of the phase inverter. Only one of the two outputs of the balun circuit may be directed to the phase inverter output, thus controlling the desired phase of the phase inverter output.
As the phase inverter is toggled between its two output states, it is important that the differential load or impedance seen by the input balun circuit always remain approximately the same; for example, one hundred ohms (100Ω). If the balun is not properly loaded as such by the remainder of the phase inverter circuit, then the phase difference between the two outputs of the phase inverter may not be 180 degrees out of phase and, thus, the output of the phase inverter may not accurately invert the phase. Also, the phase inverter input matching may degrade.
Consider an example where a phase inverter circuit comprises only an input balun circuit and a switched amplification stage at the phase inverter output. When one side of the phase inverter circuit output is switched “ON” for example, that side of the phase inverter circuit can easily match the impedance seen by the input balun circuit to 50Ω. However, the other output side of the phase inverter circuit is switched “OFF” and exhibits a relatively high impedance value as seen by the input balun circuit. As a result, in this exemplary situation the input balun circuit is not properly loaded at all times with a 100Ω differential impedance.
A balun circuit may comprise transistors (an “active” balun circuit) or the balun circuit may comprise inductors and capacitors (a “passive” lumped balun circuit). Also, baluns may comprise transmission lines in a Marchand balun structure (a “passive” Marchand balun circuit). Also, baluns may comprise other types of electrical components (e.g., transformers).
Baluns find usage in a wide range of devices, including high frequency (e.g., 60 GHz V-Band) phased array devices and transceivers for use in, e.g., radar applications. Baluns are oftentimes embodied in integrated circuits (“ICs”) or may comprise various discrete electrical components mounted on a printed circuit board. Regardless, it is desired that the phase inverter circuit that includes the input balun circuit be implemented in a relatively compact and simple manner.